Amebic dysentery

Amebic (or amoebic) dysentery , which is also referred to as amebiasis or amoebiasis, is an inflammation of the intestine caused by the parasite Entamoeba histolytica. The severe form of the malady is characterized by the formation of localized lesions, called ulcers, in the intestine, especially in the region known as the colon, abscesses in the liver and the brain, and by vomiting, severe diarrhea with fluid loss leading to dehydration, and abdominal pain.

Amebic dysentery is one of the two most common causes of intestinal inflammation worldwide. The other is infection with bacteria of the Shigella group.

Amebiasis is contracted mainly by ingesting the parasite in contaminated food or water. Person–to–person transmission is less likely, but can occur. The disease is thus most common where sanitation is poor, in the developing world. The disease is especially prevalent in regions where untreated human waste is used as fertilizer. Run–off from fields can contaminate wells contaminating the drinking water. Amebiasis can occur anywhere in the world in almost any climate, excluding polar areas and mountainous high altitudes. Even now, approximately 500 cases are reported each year in New York State.

Those infected with the parasite may develop the severe symptoms listed above, a milder condition characterized by nausea, loose bowel movements and pain in the abdomen, or sometimes no symptoms at all. The latter is a concern to others, as the asymptomatic person can still pass the parasite in his/her feces and so potentially spread the infection to others. Indeed, such transmission can persist even years after exposure to the parasite.

Entamoeba histolytica can occur in two forms. The parasite is excreted to the environment as a so-called cyst from. This form is very hardy, and is analogous to a bacterial spore. This form is designed for longevity, to preserve the genetic material of the parasite when in inhospitable environments. Once in a more favorable environment, such as the intestinal tract of humans, the cyst resuscitates and growth resumes. The active and growing form of the parasite is known as a trophozoite. It is the trophozoite that causes the symptoms of amebiasis. Some trophozoites will re-encyst and exit via the feces, to become a potential source of further infection.

If the cyst stays in the intestinal tract after being ingested then they have little adverse effect. However, if the cysts invade the walls of the intestine, ulcers and diarrhea can be produced. Amebiasis can be fairly short in duration, lasting only a few weeks. Or, the infection may become chronic. The chronic form can be ominous, as the trophozoite can invade the blood and be carried all over the body. The abscesses formed in the liver and brain can be very destructive.

Both amebiasis and the causative parasite have been known for a long time. The parasite was described in great detail and given its name in 1903. Despite this long history, the diagnosis of the malady still relies on the visual detection of the parasite in fecal material obtained from a suspected patient. Often fecal samples need to be examined for several days to detect the presence of cysts. Amebiasis is still easily misdiagnosed, especially when no symptoms are present. Also the parasite can be visually similar to harmless normal residents of the intestinal tract, such as Entamoeba coli, and can co-exist with bacteria that themselves are the cause of the symptoms being experienced by the infected person.

Amebiasis is treatable, usually by a combination of drugs. An amebicide will kill the organisms in the intestinal tract, while an antibiotic will treat any bacteria that have been ingested with the feces, contaminated water, or food. Finally, if warranted, a drug can be administered to retard the spread of the infection to tissues such as the liver.

See also Parasites